The present invention relates to methods of producing shaped articles formed of composites or laminates. More particularly, the present invention allows the formation of complex or difficult shapes out of fiber/thermoplastic resin composites while controlling the final fiber positioning.
Because of their strength, composites or laminates of fibers and thermoplastic resins are useful in the production of a number of shaped parts. These composites are primarily made of continuous or discontinuous fibers of fiberglass, graphite, carbon, polyaramides such as KEVLAR, polyethylene, or other strengthening fibers bound in a thermoplastic resin. Continuous fiber composites are frequently manufactured in the form of sheets or panels.
Unfortunately, the reinforcing fibers which strengthen the resin and give the composite additional support and structural integrity can cause problems during processing and forming operations, particularly in the manufacturing of parts having complex shapes such as rectangular boxes or spherical surfaces. When such complex shapes are formed using standard molding techniques, e.g., by heating the composite and molding it to the desired shape under pressure, the reinforcing fibers move and slide, causing some portions of the molded piece to have few or no fibers while other sections have too many fibers. This movement of fibers leads to a difference in mechanical properties at various locations in the final product. This variation in quality can lead to rejection of the part, or if the problem is less severe, overdesign of the part.
In order to prevent these problems, some complex shapes have been formed by creating the composite in situ, e.g., laying the fibers into a mold in the final shape and adding heat and pressure to soften and consolidate the thermoplastic components. This procedure is more expensive than conventional procedures and still may not solve the problem of fiber movement and the resulting property differential. Therefore, the search for better ways of forming complex molded products of composites has been continuing.
Accordingly, an object of the invention is to provide a method forming composites or laminates into desired shapes while controlling fiber movement.
A further object of the invention is to provide a method of forming a complex shape from a composite while organizing the fibers of the composite in a predetermined pattern.
Another object of the invention is to provide a method for further strengthening complex shaped articles formed from composites.
These and other objects and features of the invention will be apparent from the following description and the drawing.